The invention relates to a method of controlling a supply of ink in a printing machine, more particularly, wherein the ink is differently guided zonally on an ink-fountain roller transversely to the printing direction, and is transferred by a vibrator roller to a distributor roller, and to a printing machine for performing the method, including an electronic control device, an ink metering device and a distributor roller having a starting time that is adjustable relative to a rotational-angle setting of a printing-form cylinder.
In modern printing machines, the instant of reversal, referred to hereinafter as the application time or starting time, is adjustable relative to the phase angle of the printing-form or plate cylinder, with the distributor roller located in a dead center position beginning to oscillate in a direction towards the dead center position opposite thereto at that instant of time. Consequently, it is possible for the pressman to compensate for the fall-off in ink layer thickness over the format length, a phenomenon known as ink fading, in the printing direction. The causes for the ink fading can be a nonuniform division of subjects on the printing form and the print-free space on the printing form cylinder caused by the cylinder gap. The not as yet compensated-for ink fading can, for example, have a maximum of the ink layer thickness thereof at the printing start, and a minimum of the ink layer thickness thereof at the printing end on the printing form. In this case, by adjusting the starting time, the maximum of the ink layer thickness can be displaced from the printing start in the printing direction as far as the center of the format, so that the ink fading on the printed product is no longer perceptible with the naked eye.
In this regard, the German Published Non-prosecuted Application (DE-OS) 23 36 061 describes a device by which the beginning of the distribution of ink on distributor rollers is adjustable relative to the rotational movement of a plate cylinder.
The published German Patent Document DE 36 14 555 C2 describes a method of setting the starting time of the lateral distribution, by which the optimum starting or application time is determined directly by the computer of a measuring device.
The published German Patent Document DE 40 04 056 A1 describes a device for performing a method for controlling ink and for zonally presetting ink metering elements, wherein an oscillation phase angle of an oscillating distributor is controlled by a ghosting computer in accordance with a subject-specific inking profile that is to be expected from an original.
In all of the devices and methods described in the aforementioned published documents, the oscillatory movement of the distributor roller is controlled.
As is generally known, many printing machines include an ink metering device by which the quantity of ink supplied into the inking unit is zonally adjustable, so that the quantity of ink that is supplied can be metered differently over the format width in accordance with an inking profile suitable for the subject.
In this regard, the published German Patent Document DE 43 41 011 A1 describes a method of controlling ink by which ink is not supplied in specific zones on the ink-fountain roller. Although in this method the lateral ink flow due to the transverse distribution is taken into consideration in adjusting the ink density of individual zones, the method has no relationship whatsoever to the starting or inception time for an operating range of a distributor roller.
A drawback in this method is that, in the course of the conceivable performance thereof by a printing machine with a distributor roller having an adjustable starting time, during the adjustment of the starting time by the pressman, the zonal ink adjustment must be reset manually every time, because the ink fading and the zonal ink adjustment are actuating values which compete with one another. Especially great problems arise therefrom in label printing and in other multiple-copy work, because there is a requirement therein for all the blanks arranged on the sheet of printing material to be printed in absolutely the same hue. For example, the green hue of labels to be printed on the sheet of printing material is produced by autotypical or half-tone ink mixing of the cyan and yellow inks printed after one another. In this regard, the slightest deviations from one another of the ink layer thickness of the yellow ink on two labels are noticeable in a conspicuously disturbing manner when the hues of the two labels are compared.
The foregoing also applies to a printing device described in the Japanese Published Non-prosecuted Patent Application (JP-OS) 59-71 863, and to a method described in the published German Patent Document DE 197 11 918 A1.
In practice, the zonal ink metering device is preset initially in accordance with an inking profile suitable for a subject, for which purpose data determining the inking profile are fed to the ink metering device from a plate scanner. It is then an obligation of the pressman to adjust the starting or inception time and to correct the preset inking profile so that the hue of all the labels located within the format area is the same to the greatest possible extent. These manual adjustments are very time-consuming and laborious. If the pressman adjusts the starting time in order to balance the hue of labels located at the start of printing with the hue of labels located at the end of printing, the hue balance or equalization of labels located beside one another transverse to the printing direction is lost. In order to balance the hue on labels located at the side edges of the format to the hue of labels located at the center of the format, the printer has to correct the zonal metering again, due to which the hue balance in the printing direction is, in turn, influenced detrimentally. Balancing or equalizing the hue is particularly difficult in the case of an even-numbered, for example half-turn, vibrator cycle, in conjunction with an even-numbered, for example likewise half-turn, distributor cycle, because in this case it is additionally necessary to balance the hue of labels located on the right-hand side edge of the format with the hue of labels located on the left-hand side edge. A half-turn cycle means that the printing plate cylinder executes two revolutions for each vibrator or distributor oscillation. The pressman must adjust the starting time and the zonal ink metering in ever finer actuating steps and alternately until the pressman has found the optimum color balance of all the labels over the entire format area.
With a view to these problems, which have heretofore been unsolved in practice, it is an object of the invention to provide a method of controlling the supply of printing ink in a printing machine, wherein the pressman is relieved of lengthy setting-up operations, and to provide a printing machine for performing the method effectively.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of controlling the supply of ink in a printing machine wherein the ink is differently guided zonally on an ink-fountain roller transversely to the printing direction, and is transferred by a vibrator roller to a distributor roller, which comprises metering the ink zonally for counteracting ink transfer disturbances caused by a stroke movement of the distributor roller, so as to minimize the disturbances automatically to at least an effective extent.
In accordance with another mode, the ink transfer disturbances are at least one of ink deficiency and ink excess disturbances resulting from a change in a periodically repeating edge offset of the distributor roller with respect to the vibrator roller as ink is transferred from the vibrator roller to the distributor roller, the disturbances being located in the vicinity of the edge offset, and the method includes compensatingly adjusting the supply of ink in at least one of the inking zones affected by the ink transfer disturbances so as to effectively minimize or eliminate the ink transfer disturbances.
In accordance with a further mode, the method of the invention includes adjusting an inflow of ink into at least one inking zone close to a roller edge so as to compensate for the ink transfer disturbances.
In accordance with a second aspect of the invention, there is provided a printing machine including an electronic control device and a distributor roller having a starting time that is adjustable relative to a rotational angle position of a printing form cylinder, comprising an ink metering device zonally adjustable by the electronic control device in accordance with the starting time of the distributor roller.
In accordance with another feature of the invention, one of a distributor stroke drive and a distributor stroke drive transmission of the distributor roller is controllingly connected to the electronic control device, so that the ink metering device is zonally adjustable by the electronic control device in accordance with the one of the distributor stroke drive and the distributor stroke drive transmission, respectively.
In accordance with a further feature of the invention, the distributor stroke drive transmission has a potentiometer assigned thereto that is adjustable together with the adjustment of the distributor stroke drive transmission, and is capable of signalling to the electronic control device the amount of the adjustment of the distributor stroke drive transmission and, therewith, the starting time of the distributor roller.
In accordance with an added feature of the invention, the ink metering device includes at least one ink metering element close to a roller edge, the one ink metering element being adjustable by the electronic control device in accordance with the starting time of the distributor roller.
In accordance with an additional feature of the invention, the ink metering device includes at least one ink metering element that is adjustable both in accordance with a zonal inking profile suitable for a respective subject and in accordance with the starting time of the distributor roller.
In accordance with yet another feature of the invention, the electric control device is capable of acquiring data for determining a zonal inking profile suitable for a respective subject.
In accordance with a concomitant feature of the invention, the ink metering device is automatically adjustable in an actuating direction by the electronic control device in accordance with an adjustment of the starting time of the distributor roller, so as to compensate for inking-related effects of an adjustment of the starting time of the distributor roller relative to a rotational angle position of the printing form cylinder.
Thus, the method according to the invention for controlling the supply of ink in a printing machine, wherein the ink is guided transversely to the printing direction zonally differently on an ink-fountain roller and is transferred by a vibrator roller to a distributor roller, includes automatically compensating for ink transfer disturbances caused by the axial stroke or reciprocating movement of the distributor roller, to the greatest possible extent by adjusting the zonal ink metering. One advantage of the method is that no readjustment work is required to be performed manually, and the pressman can rely on the fact that, after the adjustment of the starting time of the distributor roller, the inking over the entire format width matches precisely as before. The method is, moreover, advantageous with regard to the controlled balancing of inking-profile distortion, the control being performed by an electronic control device. The ink-profile distortion is caused by a change, relative to the phase angle setting of a printing form cylinder, of a position of the distributor roller with respect to the vibrator roller, the position of the distributor roller being offset periodically and repeatedly in the axial direction, and relative to an inking unit roller, as ink is transferred from the vibrator roller via the distributor roller to the inking-unit roller.
In an advantageous refinement of the method, in order to develop the method according to the invention with regard to a rapidly reacting adaptation of the inking profile of an ink metering system to the newly adjusted starting time, the ink deficiency disturbance caused by the distributor stroke or reciprocating movement after the adjustment of the starting time in a specific inking zone or in a number of specific inking zones is compensated for by increasing the supply of ink into this zone or into these zones, and/or the ink excess disturbance caused by the distributor stroke or reciprocating movement in a specific inking zone or in a number of specific inking zones is compensated for by reducing the supply of ink into this zone or into these zones.
In a further refinement of the method, which is advantageous with regard to avoiding under-inked or over-inked circumferential stripes on the circumferential regions of the inking-unit roller which are close to the side edges, the ink transfer disturbances are compensated for by increasing or decreasing the supply of ink into an inking zone close to the side edge of the vibrator roller or into a number of inking zones located beside one another close to the edge of the vibrator roller.
The printing machine according to the invention, including an electronic control device, an ink metering device and a distributor roller with a starting time that can be adjusted in relation to the rotational angle position of a printing form cylinder, is distinguished by the fact that the ink metering device can be readjusted under computer control after an adjustment to the starting time of the distributor roller. With this printing machine, the method of the invention can be performed very effectively, inking disturbances caused by a changed lateral edge offset of the distributor roller being eliminated or adequately and effectively minimized by the zonal supply or withdrawal of ink, which is performed automatically and counteracts these disturbances. The ink metering device can thus be tracked under electronic control to a changed axial phase angle of the distributor roller, relative to the vibrator roller which strikes the latter, by adjusting the starting time of the distributor roller relative to the rotational phase angle of the printing form cylinder. As a result, the ink transfer that is distorted in the axial direction can be compensated for without any manual controlled intervention.
In an embodiment of the invention that is advantageous with regard to driving the distributor stroke or reciprocating movement by an electric motor or a transmission mechanism in order to develop the printing machine according to the invention, a distributor stroke or reciprocating drive or transmission of the distributor roller, and the ink metering device are coupled to one another in terms of control technology via the electronic control device, so that the ink metering device can be adjusted zonally by the electronic control device in accordance with the distributor stroke or reciprocating drive or transmission. The electronic control device includes at least one microprocessor and may include two intercoupled microprocessors, one of which is linked to the ink metering device and the other is linked to the distributor stroke or reciprocating drive or transmission and, for example, to a potentiometer thereof.
In a further embodiment, which is advantageous with regard to very precise detection of the adjustment of the starting time, the distributor stroke or reciprocating drive transmission is positively coupled to a potentiometer, which can be rotated or displaced as a result of a displacement of the distributor stroke or reciprocating drive transmission, and via which the distributor stroke or reciprocating drive transmission is linked in control-technology terms to the electronic control device.
In an embodiment that is advantageous with regard to compensating for too high or too low an optical density in the side region of the printing format, as a result of the adjustment of the starting time of the distributor roller, a metering element for controlling the ink supply in an inking zone close to the side edge of the vibrator roller, or a number of metering elements for controlling the ink supply, respectively located adjacent one another in an inking zone close to the edge of the roller, can be readjusted under computer control following an adjustment to the starting time of the distributor roller.
In a further embodiment, which is advantageous with regard to calculating a corrected rotational or advanced position of the metering element or of the metering elements based upon pairs or groups of values stored in the electronic control device and, for this purpose, determined in advance, for example empirically, a corresponding characteristic curve or functional equation, which describes the relationship between, on the one hand, the adjustment phase angle of the starting time of the distributor roller and, if necessary or desirable, in addition the necessary zonal optical density or the preset zone opening value and, on the other hand, the rotation or displacement of the respective metering element by a correction value required for correcting the inking profile, the zonal ink flow of each metering element to be readjusted results from a zone opening value, that has been corrected in accordance with the adjustment of the starting time, of the already set inking profile suitable for the subject. The correction value can be selected by the electronic control device, starting from the previously set inking profile suitable for the subject and the not yet corrected zone opening value thereof, and calculated from the adjustment phase angle or current starting time or from the stored data sets. The determined correction value may have a sign, for example depending upon the actuating direction required, positive in order to increase and negative in order to decrease the ink flow of the metering element. In the example, the electronic control device adds the correction value, with the sign thereof, to the not yet corrected zone opening value, and adjusts the metering element into a position corresponding to the result of the addition.
In an embodiment that is adapted to the different technical conditions in the pre-press stage, the zone opening values, which have not yet been corrected and which determine the inking profile of the metering elements that is suitable for the subject, can be adjusted manually on the electronic control device and can be read into the electronic control device and stored in the latter by a mobile data carrier (for example by floppy disk or magnetic tape cassette) or by a data line (for example from a plate scanner).
In a further embodiment, which is advantageous with regard to avoiding rejects or waste, the ink metering device can be tracked to the adjustment of the starting time by the electronic control device during this adjustment, so that undesired effects in the printed image, which are caused by the adjustment of the starting time, even become impossible to see.
The printing machine is preferably a sheet-fed rotary offset printing machine with a vibrator-type inking unit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of controlling the supply of ink in a printing machine, and a printing machine for performing the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: